Science of the Hazard

The Wasatch Front and outlying communities are often warned about our potential for experiencing a major earthquake. But since many Utahns have never felt an earthquake, it may be difficult to believe our area is at risk, let alone imagine what the aftermath of a serious earthquake might be.

The fact is, the Wasatch Front is a fault line—called the Wasatch fault zone (WFZ). In March of 2018 alone, the University of Utah seismograph station recorded dozens of small earthquakes, with a few at magnitudes at or near 3.0(1). A 2016 forecast by the Working Group on Utah Earthquake Probabilities puts the risk of a major (6.75 or greater) quake along the Wasatch Front at 43% in the next 50 years(2).

What causes earthquakes and why are we at risk?

Credit: GeologyPage.com

The earth’s crust is not one solid sphere. It is comprised of many plates that meet each other at fault lines much like a jig saw puzzle. Because of the convection of molten material beneath the plates, they don’t sit still. Some plate boundaries slide against each other (transform) while others push at one another (convergent) and still others pull away from each other (divergent)(4).

Within a single plate, many faults can exist. These are smaller borders where two pieces of terrain are exerting pressure upon one another. When this pressure is suddenly released, the energy sends out waves that cause the ground (and structures above it) to shake—sometimes violently. There are three types of faults: Strike-slip, Normal, and Reverse faults. The WFZ is a normal fault, meaning one part of terrain is force upward while another slides down(5). Essentially, the same mechanism that created the Wasatch mountains puts us at risk of an earthquake.